Dual-rotor motor

ABSTRACT

The invention relates to an electric motor with an outer rotor and an inner rotor, wherein the stator carrying the excitation coils is formed as a hollow cylinder and is arranged between the cup-shaped outer rotor and the inner rotor and is rigidly connected on the front to the housing or to a part of the electric motor rigidly connected to the housing, wherein the stator comprises a plurality of stator teeth which rest against supports extending in the axial direction, wherein the supports are formed by an injection moulding composition of plastics material, in particular a thermosetting plastics material which fills the space between the respectively adjacent excitation coils and the stator teeth, the supports extending into and/or through the metallic housing or a metallic part rigidly connected to the housing and rest against it.

The present invention relates to a double rotor motor according to the preamble of claim 1.

PRIOR ART

Double rotor motors which have an individual tooth technology and a high efficiency but a low strength and poor heat dissipation are known from WO 06/083097, U.S. Pat. No. 6,002,192, WO04/004098 and U.S. Pat. No. 5,982,070. These motors are characterised by a high efficiency of the magnetic circuit, since with the impression of a current in the stator tooth, a torque is generated by two rotors. Individual teeth in the exciting circuit are particularly advantageous, as stated in the above-mentioned applications.

Double rotors can be configured for high outputs and torques. For this, the excitation teeth, coils and attachments must have a high degree of rigidity. For high torques and a compact construction, the excitation teeth with coils have to be constructed close together. Since the stator is self-supporting in the case of a double rotor motor with individual teeth, the teeth and coils have to be supported on the housing with a high degree of rigidity. Furthermore, the variation in the magnetic flux in double rotor motors is very high so that electrically conductive materials are undesired in the magnetic circuit, because very high eddy currents are generated therein. For this reason, electrically conducive materials with a large cross section are to be avoided particularly in the region of the greatest changes in flux, as occur in the poles and in the air gaps.

WO2006/083097 discloses a double rotor motor of this type. In this case, the self-supporting coils are injection moulded with the coil bodies and yoke to produce a stator. The application does not show a cross section through the coils to detect the distance to the adjacent yoke. It can therefore be assumed that the illustrated wall thickness also applies in the circumferential direction and thus there is a large distance to the adjacent coil. The torque is substantially supported by the insert moulded bodies and the ribbing on the side of the housing. Since very high moments are primarily effective in the outer region, the stator can only support torques to a limited extent.

WO 2004/004098 also discloses a double rotor motor, in which the yokes are insert moulded with the coil bodies. The coil bodies are centred with the wound coils in a housing by positioning webs of a plastics material body (FIG. 13A) and then encapsulated with the plastics material body and the housing with cast resin. Since the positioning webs only have a small width, their geometrical moment of inertia Ia is very low so that the positioning webs can only transmit low forces. As is known, cast resin has a low modulus of elasticity so that high moments cannot be transmitted by the encapsulation either. The tooth is primarily supported on the coil body which, in turn, is connected to the housing and the support by the encapsulating compound. Thus, the construction can only be loaded to a limited extent and can only be used for motors with a low torque load.

Furthermore, the dissipation of heat is very limited in the case of the prior art motors, because the stator is disadvantageously connected to the housing. As shown in FIG. 9C (WO 2006/083097), the stator is connected to the radially inwardly offset housing by plastics material over a great path length. Consequently, the output of the motor is very limited, since the heat cannot be removed from the coils. Moreover, since the thermal conductivity of cast resin or injection moulded plastics material is very low, a large spacing between coil and metal housing has a thermally insulating effect. The same applies similarly to WO2006/083097.

Double rotor motors which have a high degree of rigidity and efficiency are already known from EP 1879283 (Matsushita), EP 1191673 (Denso) and U.S. Pat. No. 5,260,642 (Huss). From EP 1879283 and EP 1191673 a stator construction is in each case already known, in which two rotors provided with permanent magnets are joined to one another via a shaft. In this respect, the rotors are driven by a stator wound with excitation coils. The stator is configured as a single part and consists of inner and outer teeth with pole shoes and a tangential connecting web between the yoke arms. An excitation coil is in each case wound in the circumferential direction on each connecting web, as illustrated in FIG. 8 of EP 1879283 and in FIG. 38 of EP 1191673. Due to this coil arrangement, the magnetic flux is generated tangentially in the connecting web. The magnetic flux is at the same time divided into two magnetic partial fluxes in the yoke teeth. One of the partial fluxes goes radially outwardly to the outer rotor and is closed via the outer rotor, and goes radially inwardly via the adjacent stator tooth to the connecting web. The second partial flux leads radially inwardly and is closed via the inner rotor, and is led radially outwardly via the adjacent stator tooth and is closed via the connecting web.

In EP 1191673, in contrast to the stator structure of EP 1879283, the rotors are not joined to one another via a shaft. Instead, the relative rotor position of the outer and inner rotors is regulated by a control algorithm.

A further double rotor is known from U.S. Pat. No. 5,260,642. Here a plurality of rotors equipped with permanent magnets are arranged axially with respect to one another and are driven via an external excitation stator.

The winding technique known from EP 1191673 and EP 1879283 is disadvantageous. The tangential winding technique is on the one hand very complicated, and on the other hand a good copper space factor cannot be achieved with automated winding, since the space covered by the pole shoes is very difficult to fill during winding. In addition, the magnetic flux is generated in the tangential direction from the connecting web and is then deflected by 90° in the radial direction. This is unfavourable for the efficiency of the magnetic circuits and prevents the use of soft magnetic material with grain orientation.

OBJECT AND IMPLEMENTATION OF THE INVENTION

The object of the invention is to provide a double rotor motor for high torques and output.

This object is advantageously achieved with a double rotor motor which has the features of claim 1. Advantageous configurations of the double rotor according to claim 1 are provided by the features of the subclaims.

The invention is based on the concept that the coil supports which also form the poles and the yoke are insert moulded with a plastics material, the plastics material forming a support structure which is also formed between the individual coil supports and coils. During the insert moulding procedure, the plastics material joins with the housing or with a part connected to the housing, thereby producing a stable unit. The plastics material is preferably a high-strength plastics material. The plastics material composition injected between the coil supports forms supports in each case, the cross section of which is advantageously U-shaped, T-shaped or double-T-shaped.

The configuration of the double rotor motor for high torques, output and a compact construction requires specific solutions in terms of rigidity and heat dissipation, since the insert moulding/encapsulating alone of coil supports and yoke is not sufficient for this. For a high rigidity, a high geometrical moment of inertia Ia for a low bending of the stator and a high modulus of elasticity is required. In the prior art, the coil body was used as the support and is connected to the housing by the encapsulating compound, or an insert moulding of the stator teeth which produces the rigidity.

In contrast to this, the invention provides using the production-related space or spacing between the coils which is filled by the injected plastics material and forms a support structure or a support. This produces a geometrical moment of inertia Ia which is greater than the coil body by a factor of four. The entire yoke or the external pole can also be insert moulded with a relatively thin wall of plastics material. In contrast to the prior art, the reinforcement is supported by a high-grade plastics material. However, it is also possible for a filler with a high modulus of elasticity to be additionally injected. A thermosetting plastics material is preferably used in which an effective heat-conducting filler, for example boron-nitride is embedded. The insert moulding is connected to the housing with suitable profiled parts and anchors. The use of plastics material advantageously minimises the eddy current losses to achieve a good efficiency.

For further reinforcement, parts which are of a particularly thin-walled configuration, with a high modulus of elasticity can be embedded or incorporated in the injection moulding.

Also advantageous is a stator tooth with a body-less coil or with insulation parts only on the tooth neck wall and front with a corresponding spacing to the external and internal poles. The material is then injected into this space formed by the spacing.

All the individual yokes with their coils are connected to the housing and centred accordingly by the previously described insert moulding procedure. The free space or spacing between the coils and yokes, like the front of the coil, is then sheathed or filled with plastics material, it being possible for a corresponding structure and contour of the plastics material with respect to the outer reinforcement to be formed.

In a particularly advantageous configuration of the invention, the free space or spacing between the individual yokes and the coils forms a double-T-support-shaped space which is filled by the plastics material. Thus, after injection, the plastics material forms in cross section a double-T-support-shaped support which is anchored in the housing or in the part joined to the housing. A particularly good rigidity is thus achieved by this cross-sectional contour. The cross-sectional contour of the supports can advantageously extend into the correspondingly formed recesses in the housing or in the part joined thereto, thereby producing a particularly good rigidity of the supports. In this respect, the cross-sectional area of the recesses can be larger than the support cross-sectional area in the region of the rotor, so that a type of widened base is produced on the support which extends into the recesses in the housing or housing part.

Likewise, to reinforce the plastics material composition, reinforcing elements can be provided, one end of which extends in each case up into a recess and the other end extends as far as the stator tooth or up into the gap between the adjacent stator teeth. In this respect, the reinforcing elements can be embedded in the region of the external pole shoe and/or the internal pole shoe.

It is optionally possible to obtain an even more rigid construction by additionally insert moulding the poles with the plastics material. The plastics material sheathing the poles or pole shoes is joined to the supports by radially and axially extending walls. Although the length of the air gap is increased by the sheathing of the pole shoes, this is compensated by the increased rigidity and thus the greater power of the motor.

In the embodiment according to the invention, individual stator teeth which in cross section can advantageously have a double-T shape, i.e. they have radially outer and inner pole shoes, are initially wound axially and then positioned in the injection moulding die. Unlike double rotors with a high output and rigidity (prior art (EP 1879283 (Matsushita), EP 1191673 (Denso) and U.S. Pat. No. 5,260,642 (Huss)), the stator does not have any tangential connecting webs. In this embodiment, the magnetic flux is generated radially and is closed via the outer rotor, the adjacent stator teeth and the inner rotor.

The individual teeth are firmly anchored to the housing and are held in position by the supports and support elements injected from plastics material.

The injected support elements are preferably T-shaped of more preferably double-T-support-shaped so that the stator is provided with a very high rigidity for radial and tangential loads. To ensure a very efficient heat dissipation, the plastics material is preferably formed from materials which have a high thermal conductivity but a low electrical conductivity.

The construction according to the invention has the following advantages over the prior art:

-   -   greater efficiency of the motor due to radial flux generation in         the excitation yoke;     -   very high power density due to the double rotor;     -   simple and cost-effective winding technique due to individual         tooth winding technique;     -   cost-effective motor construction;     -   very high copper space factor due to individual tooth winding,         use of rectangular wire or shaped wire possible;     -   use of grain-oriented material or sheet metal material with         preferred direction in individual teeth possible due to radial         flux generation in the stator;     -   very good heat dissipation is possible if the coil is arranged         in a highly thermally conducting support, and the pole shoes of         the stator teeth are in contact with the housing;     -   coils can be checked before installation;     -   good radial and tangential rigidity;     -   simple electrical contacting of the coil on the rear of the         housing and in recesses of the housing;     -   possibility of configuring a highly dynamic motor by minimising         the inertial mass of the rotors by a double air gap and         thin-walled rotor configuration.

In the following, various embodiments of the double rotor motor according to the invention are described with reference to drawings, in which:

FIG. 1 shows the motor construction according to the invention with an optional outer and inner back-circuit element;

FIG. 1 a is a plan view of the reinforcing element;

FIG. 2 is a partial cross-sectional view through stator, outer rotor and inner rotor with a support structure injected from plastics material;

FIG. 2 a shows a support structure with a reinforcing element;

FIG. 2 b is a sectional view of the housing part and of two supports;

FIG. 2 c shows the motor with externally and internally insert moulded pole shoes.

FIG. 1 is a cross-sectional view through a first possible embodiment of the motor according to the invention along line x-x in FIG. 2. The support structure 35, 35 a, 35 b, 35 c consists of a high-grade, bending-resistant and, at the same time, electrically insulating material with a high modulus of elasticity, preferably a thermosetting plastics material with filler. The cross-sectional contour of the individual supports 35, formed by the injected composition, is shown in more detail in the following figures. Positioned in the injected composition of the support material is the coil 4 with yoke 1 and is held by said injected composition on the housing 12. The insert moulded structure 35 which forms the individual supports has on the housing side a respective thickening 35 a in the form of a base which extends up to the axial side 1 a of the yoke 1 and is anchored in the housing 12 in a corresponding recess 12 b. The insert moulding can preferably be carried out in two steps so that a different filler with better heat conducting properties, for example boron nitride, is introduced in region 35 a and a filler with a high modulus of elasticity, for example glass fibre-reinforced plastics material is introduced in region 35. This can further improve the heat dissipation between stator and housing.

The stator consists of individual stator teeth 1 with pole shoes 1 a in the outer region and pole shoes 1 b in the inner region, which are wound with excitation coils 4. In addition, the motor comprises an outer rotor 3 a provided with permanent magnets 2 a and an inner rotor 3 b provided with permanent magnets 2 b. Furthermore, two back-circuit elements 24 a, 24 b are shown which are optional. The back iron can also take place via the rotors 3 a, 3 b. Air gaps 1 f are in each case between the pole shoes 1 a, 1 b and the rotors 3 a, 3 b as well as the optional back-circuit elements 24 a, 24 b.

A pressed screen 23 can also be provided which is also insert moulded for contacting purposes, so that the contacting of the coils 4 takes place before the insert moulding procedure and thus the tool configuration is simplified. In a multi-part injection process, it is to be provided that the injection moulding compositions interlock. A corresponding interlocking region and separating region of the moulded compositions is shown at 35 d.

Furthermore, the housing 12 in region 12 a is to be configured such that the spacing between coil side 4 a and housing region 12 a is minimised. Therefore, the housing region 12 a widens towards the rotation axis to be adapted to the coil contour. This ensures that the wall 35 w, produced by insert moulding, is as thin as possible for a good heat transfer. The wall region 35 w can also be produced by a plastics material with good heat conduction properties.

Injection moulded on the inside is a reinforcing insert 36 with a high modulus of elasticity and heat conduction which, during injection moulding, is pressed positively onto the stator teeth 1 by suitable tools. In addition, a further outer insert part 37 is optionally provided which is also joined to the injection moulding in region 35 c by one or a plurality of recesses 40 also in the inner insert part. A connecting web or connecting ring 38 can also be provided between the insert parts 36 and 37 for further reinforcement.

The insert part 36, 37 can also project laterally out of the housing 12 and rest resiliently against the housing 12 to maintain a bias. This improves the bond, in particular when a metallic material is used as the insert parts 36, 37. To reduce eddy currents, the insert part 36, 37 is thin and is provided with stamped-out elongated slots 37 a, as shown in FIG. 1 a.

On the front 4 b, remote from the housing, the coil 4 is also insert moulded, the injection composition forming reinforcing ribs 35 b. These enhance the rigidity and enlarge the surface for heat dissipation by air cooling. The air cooling is furthered by a fan impeller 21. For an appropriate air guidance, recesses 39 can be made in the rotor and in the housing 12.

The magnetic back irons 24 a and 24 b are mounted such that they are fixed to the housing. There are two air gaps if in each case between stator, rotors 3 a and 3 b and back irons 24 a and 24 b. The rotors 3 a and 3 b are configured with thin walls. This reduces the mass of inertia of the rotor and the cooling channels 18 can extend axially in the housing, thereby improving the rotor cooling.

The support structures 35 configured as double-T supports extend as far as the inside of the yoke to increase the geometrical moment of inertia Ia and thus to improve the tangential load. For a radial load, the radial web height of the supports 35 is to be configured as high as possible, which results in a high degree of rigidity.

For the structure, it is necessary for the stator tooth to be previously wound and positioned relative to the housing.

FIG. 1 a shows the double-T support 35 with a radially outer reinforcing element 37. Alternatively, the reinforcing element 37 can be arranged relative to the excitation coils 4, but can also be arranged radially inside. Of course, reinforcing elements 37 can also be arranged outside and inside and injection moulded. The reinforcing element 37 is preferably made of a poorly conductive metallic material, for example stainless steel, with stamped-out areas 37 a to reduce the current conductivity and thus the eddy current losses.

FIG. 2 b shows the cut-off T-supports 35 with a thickening 35 a as well as the contour of the housing recess 12 b which is configured in terms of injection moulding so that a high degree of rigidity is obtained. The contour of the housing recess 12 b should correspond to the cross-sectional contour of the supports 35, so that a high degree of rigidity results and the supports extend up into or through the housing wall. In this respect, attention should also be paid to a minimum use of material, while bearing in mind the necessary rigidity.

FIG. 2 c shows a widening of the T-support structure 35. The supports 35 are connected to an outer ring 35 e as part of the injection moulding over the regions 35 s, which comprise the external poles 1 a including the outer reinforcing ring 35 e. Even in the case of a small wall thickness, this ring 35 e is also very effective for reinforcement with a tangential load. In region Z-Z, a further alternative is shown, in which both the external and the internal yoke poles 1 a, 1 b are insert moulded through rings 35 e in a thin-walled manner and are connected to webs between the coils. A thermosetting plastics material is preferably suitable for producing a thin wall thickness. For the injection procedure, the region E between the poles can be configured to be slightly recessed if appropriate due to the formation of burrs.

As a result of the above-mentioned measures, the coil space between the poles can be fully utilised, which increases the efficiency. These measures make it possible to achieve a great rigidity with good heat dissipation, so that it is possible to realise a motor with high output, a small diameter and relatively long self-supporting coils.

LIST OF REFERENCE NUMERALS

-   1 Pole shoe moulded part as stator tooth -   1 a Outer pole shoe of the pole shoe moulded part or stator tooth -   1 b Inner pole shoe of the pole shoe moulded part or stator tooth -   1 f Air gap -   2 a Permanent magnets of the outer rotor -   2 b Permanent magnets of the inner rotor -   3 Rotor -   3 a Outer rotor -   3 b Inner rotor -   4 Excitation coil -   11 Cooling channel -   12 Housing -   12 a Housing shoulder -   15 a, 15 b Shaft bearing -   16 Driven shaft -   18 Water channel -   21 Fan impeller -   22 Housing recess for electrical connection/coil outgoing lines -   23 Pressed screen -   24 a, 24 b Ferromagnetic housing insert part (back-circuit for     magnetic circuit) -   25 Driver -   27 Reinforcing web of double T-shaped profiled support 35 -   35 Support of the support structure from injection moulding     technique -   35 a Housing-side thickening of the injection moulding structure -   35 b Front ribbing of the injection moulding structure -   35 s Radially and axially extending connecting webs -   35 w Thin-walled region of the injected plastics material -   36, 37 Reinforcing elements -   37 a Recesses, in particular stamped-out areas -   38 Connecting web/connecting ring -   E Injection region -   Ia Geometrical moment of inertia 

1. An electric motor, comprising: an outer rotor having a cup shape, an inner rotor, and a stator, wherein the stator is configured to carry excitation coils, is formed as a hollow cylinder, and is arranged between the outer rotor and the inner rotor, and is connected on a front side to a housing or to a part of the electric motor rigidly connected to the housing, wherein the stator comprises a plurality of stator teeth which rest against supports extending in an axial direction, wherein the supports are formed by an injection moulding composition that fills space between respective adjacent excitation coils and the stator teeth, the supports extending into and/or through the housing or a metallic part rigidly connected to the housing and resting against it.
 2. The electric motor according to claim 1, wherein the supports have a cross-sectional shape which is T-shaped or double-T-shaped.
 3. The electric motor according to claim 1, wherein the stator teeth have radially inwardly directed pole shoes and radially outwardly directed pole shoes, the injection moulding composition being located between the radial side regions of the excitation coils and the insides of the pole shoes and forming tangential walls.
 4. The electric motor according to claim 1, wherein the cross-sectional area of the supports is greater in the region between housing or part and stator tooth and/or excitation coil than the cross-sectional area of the supports in the region between the adjacent excitation coils and/or stator teeth.
 5. The electric motor according to claim 1, wherein the housing or the part has a wall with recesses configured to anchor the supports.
 6. The electric motor according to claim 5, wherein a contour of the recesses corresponds to the cross-sectional contour of the supports.
 7. The electric motor according to claim 5, wherein the cross-sectional area of the recesses is greater in each case than the cross-sectional area of the supports in the region between the adjacent stator teeth and/or excitation coils.
 8. The electric motor according to claim 1, wherein the housing or the part is made of aluminium and is produced as a die-casting part.
 9. The electric motor according to claim 1, wherein the supports are connected radially outwards and/or radially inwards to an injection moulding composition which sheathes the external pole shoes and/or the internal pole shoes.
 10. The electric motor according to claim 1, further comprising reinforcing elements embedded in the injection moulding composition which forms the supports.
 11. The electric motor according to claim 10, wherein a first reinforcing element is positively connected to the stator tooth.
 12. The electric motor according to claim 10, wherein a second reinforcing element extends over part of the axial length of the supports in said supports or extends below or above the supports.
 13. The electric motor according to claim 10, wherein the respective reinforcing elements have at least one window-type reach-through opening.
 14. The electric motor according to claim 10, wherein the reinforcing elements are made of electrically non-conductive material or material which is only slightly conductive.
 15. The electric motor according to claim 10, wherein the reinforcing elements interlock with the injection moulding material via their reach-through openings and/or are connected to one another by a connecting web/connecting ring.
 16. The electric motor according to claim 1, wherein a wall of the housing or part which adjoins the axial side of the excitation coils is adapted to the contour of the side such that only a thin wall of injection moulding composition separates the excitation coils and the housing or part.
 17. The electric motor according to claim 1, wherein an axial free stator end which is remote from the housing or part has reinforcing ribs which are formed from the injection moulding composition forming the supports.
 18. The electric motor according to claim 1, wherein an axial free stator end which is remote from the housing or part has at least one reinforcing ring that is at least partly embedded in the support material and connected to the stator teeth.
 19. The electric motor according to claim 1, wherein a first outer back-circuit part comprises the outer rotor, and wherein a second inner back-circuit part is comprised by the inner rotor, an air gap being in each case between the first outer back-circuit part and the outer rotor and between the second inner back-circuit part and the inner rotor.
 20. The electric motor according to claim 19, wherein the back-circuit parts are arranged on the housing or on the part.
 21. The electric motor according to claim 1, wherein the injection moulding composition forming the supports, and which forms sheathings, consists in certain regions of different materials, wherein in regions in which a good thermal conductivity is required, a material with good thermal conduction properties is injected, and wherein in regions in which a high degree of rigidity is required, a high-strength material is injected, and wherein the injected compositions in regions interlock through undercuts so that the support encapsulating compound is supported axially, radially and tangentially on the encapsulating compound with a higher coefficient of thermal conductivity.
 22. The electric motor according to claim 1, wherein cooling channels extend in an axial direction through the housing.
 23. The electric motor according to claim 1, wherein the excitation coils do not have a winding body.
 24. The electric motor according to claim 1, wherein a filler with a high thermal conductivity is contained in the injection moulding composition to provide a high thermal conduction property.
 25. A method for producing an electric motor according to claim 1, comprising: introducing the housing or a stator flange of the motor into an injection moulding device; positioning pole shoe parts with the excitation coils relative to the housing or the stator flange; pressing a plastics material injection moulding composition into the injection moulding device to enable the plastics material injection moulding composition to penetrate and penetrates into recesses and/or undercuts in the housing or the stator flange and also into gaps between the pole shoe parts and the excitation coils, thereby producing the supports which are connected to the housing or the stator flange.
 26. The method according to claim 25, further comprising moulding reinforcing parts into the injection moulding composition.
 27. The electric motor according to claim 1, wherein the injection moulding composition is a plastic material.
 28. The electric motor according to claim 10, wherein the reinforcing elements are plate-shaped or curved plate-shaped elements that extend in an axial direction. 